The present invention relates to the production of whey protein concentrates having an enhanced .alpha.-lactalbumin content.
The isolation of individual proteins from various starting materials is well known. Most individual proteins are recovered from a mixture thereof by using differences in the physical and/or chemical properties of the proteins to advantage. Such isolation processes have usually required a multi-stage process with its attendant expense and difficulty in scaling up to an industrial process.
Whey contains many proteins with excellent properties which are also of a high nutritional value. Their large scale production in the form of wey protein concentrates only became possible with the advent in the early 1970s of ultrafiltration technology, and they have become increasingly important in satisfying the needs of the food, dietetic and pharmaceutical industries. Whey protein concentrates in power form containing all the whey proteins are currently produced by membrane ultrafiltration followed by spray drying. The concentrates generally have a protein content ranging from 35% to 85%, although lesser or greater amounts of protein can be present.
Such concentrates contain residual non-centrifugeable lipids, principally phospholipids, together with milk lipids and some phospholipoproteins. These lipoproteins concentrate at the same rate as the other proteins and have amphoteric and amphiphilic properties which lead to their being strongly adsorbed on membrane materials used in ultrafiltration, which was reported to cause irreversible fouling. For this reason Lee and Merson (J.Food Sc.41, 402-410) suggested prefiltration of whey to reduce this fouling.
Numerous methods have already been proposed to separate individual whey proteins, but most have not been capable of scaling up to industrially viable processes because of their complexity, their cost in energy, their very low yield and the irremediable degradation of the products due to the use of intensive heat treatments (Nielsen et al., J.Dairy Science 56 76-83 1973) very alkaline pH (Harris and Yoell, 1985) or of high amounts of salts (Kuwata et al., J.Food Science 50 605-609 1985).
Pearce (Aust.J.Dairy Technol. 38 144-149 1983) has proposed purification of .alpha.-lactalbumin based on the low pH solubility of .alpha.-lactalbumin under a light heat treatment. However, the .alpha.-lactalbumin fraction produced by this process has been reported by J.L. Maubois et al. of the Dairy Research Laboratory I.N.R.A. at the WPI/IDF International Whey Conference in Chicago, 27th-29th Oct. 1986 to be unsatisfactory due to the high degree of association of the whey lipids and lipoproteins with .alpha.-lactalbumin.
J.L. Maubois et al proposed a clarification process which produces a clarified whey which, when subjected to ultrafiltration produces a whey protein concentrate which they suggest is the right product for separation of individual proteins therefrom.
The clarification process has as its object the removal of the lipoproteins using their ability to aggregate through calcium bonding under heat treatment. The clarification process involves six stages which are:
1. cooling the whey to a temperature of 2.degree. C.; PA1 2. adjusting the calcium content to 1.2g/kg by addition of CaCl.sub.2; PA1 3. raising the pH of the so-treated whey to 7.3 by addition of NaOH; PA1 4. rapidly raising the temperature of the so-treated whey to 55.degree. C.; PA1 5. maintaining the whey at this temperature for a period of eight minutes; PA1 6. separating the supernatant from the precipitate by tangential microfiltration (Maubois et al indicated that tangential microfiltration was resorted to because filtration through screen plates led to loss of lipoproteins to the filtrate, and centrifugation was found to be hopelessly inefficient).
The whey, clarified in the above rather complex manner was then subjected by Maubois et al to ultrafiltration to produce a whey protein concentrate. To obtain .alpha.-lactalbumin from this concentrate they chose the method described by Pierre & Fauquant in Lait (1986). The details are fully set out in the Maubois et al publication. The method involves the gelling of .alpha.-lactalbumin by heating to 55.degree.-65.degree. for 30 minutes at a pH of .about.4 for concentrates having an .alpha.-lactalbumin content of more than 2g/kg. Maubois et al observed that the supernatant resulting from the gelling contained .beta.-lactogloubulin and that this could be realized in high purity by diafiltration on a UF membrane having a molecular weight cut off of 50,000. For separation of .beta.-lactoglobulin from the gelled .alpha.-lactalbumin however, they suggested only that the tangential membrane microfiltration technique used by them for clarification of the heat treated whey might be attempted.
Thus, whilst ultrafiltration has been suggested as one step in a process which involves a number of other physicochemical methods, for the separation of fractions containing enhanced concentrations of individual whey proteins, the method of purification as a whole has also involved a variety of other procedures which, when scaled up to produce an industrial process, become both complex and expensive to run.
Thus the provision of a simple and commercially viable process for fractionating whey proteins and in particular .alpha.-lactalbumin, has eluded the researchers.